U.S. Pat. No. 3,354,129 discloses a basic process for the production of arylene sulfide polymers from polyhalo-substituted aromatic compounds by reaction with an alkali metal sulfide in a polar organic solvent. Since then much work has been done to provide methods of modifying or controlling the melt flow rate of arylene sulfide polymers thus produced. For example, the use of curing or chain extension reactions are known for decreasing the melt flow rate. In addition, the use of alkali metal carboxylates and/or polyhalo-substituted aromatic compounds having three or more halogen atoms per molecule in the polymerization reaction mixture also is known to reduce melt flow rate. On the other hand the use of excess dihalo-substituted aromatic compound reactant is also known to provide arylene sulfide polymers of increased melt flow rate.
It is generally considered that a melt flow rate is inversely related to polymer molecular weight. Extrusion rate is a specific type of melt flow rate particularly useful for characterizing arylene sulfide polymers in the lower molecular weight range. As used herein, the term extrusion rate refers to a flow rate measurement on molten polymer based on ASTM D1238, Procedure B-Automatically Timed Flow Rate Measurement, Condition 315/0.345, using a five minute preheat time and an orifice having the dimensions of 0.0825.+-.0.0002 inch diameter and 1.250.+-.0.002 inch length.
There is a growing need for arylene sulfide polymers of high extrusion rate for use in applications such as encapsulation of electronic components and in coatings formulations. Current methods for reproducibly preparing such arylene sulfide polymers of high extrusion rate suffer from various drawbacks such as the need for recycling excess reactants which can entail costly added separation steps.
It is therefore an object of this invention to provide a method for producing arylene sulfide polymer of a desired extrusion rate in a readily controllable manner. It is another object of this invention to provide a method for producing arylene sulfide polymer having a high extrusion rate. It is another object of this invention to provide a method for producing poly(p-phenylene sulfide) having an extrusion rate of about 50 to about 1,000 g/10 min.